In recent years, a group-III nitride semiconductor, such as gallium nitride (GaN), has drawn attention as a semiconductor material capable of achieving a semiconductor light emitting element, such as a light emitting diode or a laser diode that can output high-quality light with a short wavelength. The semiconductor light emitting element is manufactured by forming a laminated structure made of a group-III nitride semiconductor on a substrate using a crystal growth technique, such as a metal organic chemical vapor deposition (MOCVD) method or a molecular beam epitaxy (MBE) method.
A known crystal growth technique, such as MOCVD or MBE, has high controllability in the laminated direction when the laminated structure is formed. In order to form a structure along the in-plane direction of the substrate, it is necessary to process the laminated structure using a crystal processing technique. The crystal processing technique is roughly divided into a top-down type and a bottom-down type. The top-down type is a technique that processes a crystal to form a structure after crystal growth. The bottom-up type is a technique that processes a base substrate in advance before crystal growth and grows a crystal on the base substrate, thereby forming a structure simultaneous with the crystal growth. The top-down process has a problem in that a crystal is likely to be damaged by processing and particularly, when a microstructure is formed, the surface area of the microstructure increases. The bottom-up process can easily obtain both a microstructure and good crystal quality.
Patent Document 1 (Japanese Patent Application Laid-Open No. 2008-108924) discloses a method of forming nanometer-scaled fine columnar crystals (nanocolumns) on a substrate using the bottom-up process. In the method, a large number of island-shaped Fe particles are formed on a spinel substrate and GaN nanocolumns are grown from each Fe particle to the upper side of the substrate. For example, a method of forming the nanocolumns is disclosed in Non-patent Document 1 (M. Yoshizawa et al., Jpn. J. Appl. Phys., Vol. 36, No. 4B (1997) pp. L459-L462) or Non-patent Document 2 (H. Sekiguchi et al., Journal of Crystal Growth, 300 (2007) pp. 259-262) in addition to Patent Document 1.